(1) Field of the Invention
This invention relates to humidifiers of the type for use in providing humidified gases to a user such as a patient requiring humidified gases. The humidifier of this invention may be used in a hospital environment but has been devised particularly for use in a home care environment.
(2) Description of the Prior Art
Humidifiers in which gases to be breathed by a patient are humidified by being passed over a heated water bath are known. Generally in this type of humidifier, particularly when used in a hospital environment, gases are regulated to a fixed, preset temperature for supply to the patient, or the water bath temperature is regulated, or an open loop controller may regulate power to the water bath. In a hospital environment, where the ambient temperature of the atmosphere within the hospital is controlled by air conditioning for example, the required temperature for the humidified gases supplied by the apparatus may be controlled within set temperature parameters. The controlled temperature parameters ensure that the humidified gases are sufficiently close to the ambient temperature to prevent condensation within the breathing conduit which supplies humidified gases to the patient but at a sufficiently high temperature to be comfortable and effective when supplied to a patient at the end of the conduit.
Humidifiers are often used in a home care environment for use such as the treatment of breathing and sleep apnea disorders and/or with ventilators.
In the home care environment the range of ambient and gas temperatures may well exceed that of the hospital environment. In the home care environment temperatures as low as 10.degree. C. may be present overnight and temperatures over 20.degree. C. may exist during the day. These temperature variations cause the commonly employed control techniques described above to suffer disadvantages.
With the types of humidifiers described, condensation (or rain out) in the breathing conduit will exist, to some degree or other. The degree of condensation is strongly dependent on the ambient temperature, being much greater for greater differences between the ambient temperature and the gas temperature. The formation of large quantities of water in the breathing tubing causes considerable inconvenience to the patient, may accelerate cooling of the gas, may eventually occlude the tubing, or may be expelled into the patient. Also, the patient may experience discomfort when breathing gases which are delivered at temperatures widely divergent from that of the ambient temperature. Excessive condensation also results in inefficient usage of the water in the humidifying chamber of the humidifier.